This invention relates to modified, water-dilutable olefin polymer oils containing carboxyl groups which are obtained by reacting .alpha.,.beta.-unsaturated monocarboxylic and/or dicarboxylic acids or their anhydrides, (semi) esters and/or (simi)amides, more especially maleic acid anhydride, with olefin polymer oils substantially free from carboxyl groups. The invention also relates to a process for producing the aforementioned modified olefin polymer oils. Finally, the invention relates to aqueous coating compositions, more especially for electro-dip lacquering, which contain the aforementioned modified olefin polymer oils as binders. These aqueous coating compositions are produced by neutralising the aforementioned modified olefin polymer oils with a base and gradually diluting them with more water, or optionally in conjunction with solvents.
The increasing demands which electro-dip-lacquers are called upon to satisfy, especially with regard to converage and protection against corrosion, are forcing the lacquer industry to turn away from the hitherto conventional, modified natural oil products. Protection against corrosion can be improved by using modified, water-dilutable olefin polymer oils which are not hydrolysable. These olefin polymer oils are preferably conjugated diolefin polymer oils which are reacted with .alpha.,.beta.-unsaturated carboxylic acids, such as acrylic acid or maleic acid anhydride, and reach a high level of water solubility by salt formation (cf. German Pat. No. 1,026,900 and U.S. Pat. No. 2,634,256, column 6, lines 67-68). Maleinised products which are unsuitable for electro-dip-coating are obtained by the methods described in these patents. Excessive viscosities in conjunction with inadequate acid numbers have such an adverse effect upon the electrical properties (deposition voltage, bath conductivity, layer resistance) of the lacquer that it is not possible to obtain optimum coating results.
German Auslegeschrift (DAS) No. 1,929,593 and German Offenlegungschrift (DOS) No. 2,120,962 describe the use of maleinised butadiene oils with water-soluble phenolic resins. According to the examples of these two specifications, very low deposition voltages are applied (100 to 150 volts for a layer thickness of 26 to 28.mu. with a deposition temperature of 25.degree. C, and a coating time of 1 minute), which gives inadequate coverage. A reduction of the high phenolic resin content is desirable not only for improving the mechanical and corrosion-inhibiting properties (cf. DOS No. 1,120,962, page 3, lines 30 to 31), but also for improving environmental conditions.